Furfural recovery



Filed Feb. 8, 1945 Patented Dec. 17, 1946 FURFURAL RECOVERY BertrandJesse Mayland Bartlesville, Okla., as-

signor to Phillips Petroleum Company, a corporation of DelawareApplication February 8, 1945, Serial No. 576,849

9 Claims. (Cl. 260-347) This invention relates to the recovery offurfural from admixture with hydrocarbons boiling above the hydrocarbonfor which the furfural has been used as an extraction agent, especiallyfrom furfural-hydrocarbon mixtures from which the furfural is notreadily removable by ordinary fractional distillation either because ofthe formation of azeotropes or because of the closeness of the boilingpoints of the furfural and hydrocarbons.

In the extractive distillation of unsaturated aliphatic hydrocarbonsusing furfural as the solvent, especially in the recovery of olens anddioleflns particularly normal butylenes and/or butadiene, the furfuralgradually becomes contaminated with close-boiling hydrocarbons which areobjectionable for a number of reasons. One diilculty caused by thepresence of a substantial amount of these oils in the furfural solventis that they cause the furfural to foam in the eX- tractive distillationcolumns and in the strippers thereby interfering seriously with theiroperation and causing loss of valuable furfural overhead. Thesehydrocarbon contaminants having boiling points above that of thehydrocarbon for which the furfural is used as an extraction agent tendto accumulate in the furfural, since they are not removed inconventional furfural re-running operations which are commonly conductedin accordance with U. S. Patents to Buell et al. 2,350,- 584, andHachmuth 2,350,699, and in Hachmuth copending application Ser. No.460,874, filed Oct. 5, 1942, such re-runnlng effecting only the removalof polymer from the furfural in the system.

These hydrocarbons may enter the system from valve, compressor, pump,etc., lubricating devices and from traces of heavy hydrocarbons retainedin the feed to the extractive distillation step. The hydrocarboncontaminants may comprise butadiene cyclic dimer (4 vinylcyclohexene-l')formed in the extraction of butadiene-containing streams. In time thesehydrocarbons may accumulate to objectionably high concentrationsresulting in a decrease in the selectivity and capacity of the furfuralto function as a selective solvent in the solvent extraction process forwhich it is being used. Also, such hydrocarbon contaminants have atendency to cause foaming in the extractive distillation and strippingsteps. Foaming decreases the eifectiveness of the furfural for makingthe desired separation because foam from the lower part of theextractive distillation column will be entrained by the upwardlyl risingvapors and carried into the upper parts 2 of the column.4 Throughfoaming and entrainment furfural may be carried overhead in thehydrocarbon products from the extractive distillation and strippercolumns resulting in a loss of furi'ural and contamination of thehydrocarbon products.

Various methods for removing these hydrocarbon contaminants fromfurfural have been heretofore disclosed. For example, the copendingapplication of Thodos and Weinaug, Ser. No. 546,- 371, filed July 24,1944, discloses the use oi light hydrocarbons such as isopentane, normalpentane, hexane, etc., in excess of their solubility in furfural at somepredetermined temperature. The light hydrocarbon and furfural areintimately mixed and phase separation allowed to occur wherein a lighthydrocarbon-rich and a furiuralrich phase are obtained. Most of thecontaminating hydrocarbons by reason of their greater solubility in thelight hydrocarbon remain in the light hydrocarbon phase. Thus afurfural-rich phase relatively free of contaminating hydrocarbons isobtained. y

The copending application of Thodos, Ser. No.

572,532, led January 12, 1945, shows a method of removing both polymerand foaming oils from furfural by extraction with light hydrocarbonwhich leaves the polymer undissolved followed by cooling of the extractphase of hydrocarbon and furfural to effect separation into two layers,namely, a furfural layer relatively free of foaming oils and ahydrocarbon layer containing most of the foaming oils.

The copending application of Weinaug and Buell, Ser. No. 576,852, ledFebruary 3, 1.945, shows a method of recovering furfural from admixturewith close-boiling oils by water extraction with such an amount of waterthat all of the furfural can readily dissolve in the water at thetemperature of extraction which preferably lies between and 150 degreesF. followed by azeotropic fractional distillation of the water extractto give an overhead of the azeotrope of furfural and water which uponcondensation separates into two layers. By the use of an excess of waterin the extraction step over that required to dissolve all of thefurfural the loss of furfural by its remaining dissolved in thehydrocarbon phase is minimized and 'the necessity for the use of hightemperatures which are objectionable is eliminated. The furfural beingmuch more soluble than the hydrocarbon in Water is selectively dissolvedto give two phases, a hydrocarbon contaminant-rich phase and a waterfurfural-rich phase. The present invention relates to an improvementover this method of water extraction.

The hydrocarbon contaminant-rich phase in all the foregoing cases willcontain appreciable amounts of furfural and the present invention isparticularly applicable for recovering the small amounts of furfuralremaining in the hydrocarbon-rich phases from the above describedprocesses for purifying furfural in admixture with close-boilinghydrocarbons. However, the process of the present invention may beequally well applied to the recovery of furfural by the water extractionmethod before any such hydrocarbon contaminant concentrate is preparedand in the latter aspect it is an improved way of carrying out the waterextraction method.

The principal object of the present invention is to provide an improvedmethod of recovering furfural from admixture with hydrocarbon' andparticularly close boiling hydrocarbons from which it is diiiicult orimpossible to separate the furfural by distillation such as fractionaldistillation or steam distillation. Another object is to provide animproved method of carrying out the water extraction of furfural fromsuch mixtures. Another object is to provide an improved methodcomprising water extraction followed by azeotropic distillation of thewater extract for recovering furfural from such mixtures. Another objectis to accomplish the foregoing objects in a simple and economical manneremploying equipment which is simple and not excessively expensive andadapted to operation for long periods of time. Numerous other objectswill hereinafter appear.

The accompanying drawing portrays diagrammatically one arrangement ofequipment which may be used for carrying out the present invention.

I have found that furfural containing hydro-1v carbon contaminantshaving higher boiling temperatures than the hydrocarbon for which thefurfural has been used as an extraction agent, especially hydrocarbonsdifficult or impossible to separate from furfural by fractionaldistillation either because of their close-boiling nature or by reasonof the formationof azeotropes between them and furfural, may be moreeasily freed of these hydrocarbon contaminants by Water extractionprovided a light hydrocarbon is present in the extraction zone.

As the light hydrocarbon employed in accordance withthe presentinvention, it is' preferred to use a hydrocarbon having not more thaneight carbon atoms per molecule and which is vcapable of existing as aliquid under the conditions of the extraction. 'Ihe hydrocarbon shouldbe lowerboiling or lighter than furfural and hydrocarbons having notover eight carbon atoms per molecule meet these requirements. Aliphatichydrocarbons are preferred. In general, any aliphatic hydrocarbon havingfrom three to eight carbon atoms may be employed. The hydrocarbon may bea paraffin or an olefin, the paraflns being preferred because of theirinertness and lower solubility for furfural. While in extreme cases adioleiin such as butadiene might be used, in general, the diolens arenot preferred because of expense, excessive solubility for furfural, andother considerations. Examples of suitable hydrocarbons are:A propane,propylene, n-butane, isobutane, n-pentane, isopentane, normal hexane,etc., up to octanes and octylenes. The lighter the hydrocarbon the moresatisfactory it is. Thus pentane is preferred to octane. While propane,may be used in the extraction its use may necessitate excessively highpressures at the extraction temperature in order to hold it in theliquid phase, although the hydrocarbon contaminants in the furfuralexhibit considerable solubility for the propane so that the pressurerequired to keep the propane in solution in the liquid higher-boilinghydrocarbons is not as high as it would be to maintain pure propane inliquid phase at the same temperature. One advantage of a normallygaseous material such as propane or butane is that it can be very easilyseparated from the heavy hydrocarbon-containing phase, In general,normal pentane is most highly preferred as the light hydrocarbon sinceit meets the foregoing requirements or desiderata better than any otherhydrocarbon.

Instead of a single light hydrocarbon, mixtures of two or more of theforegoing hydrocarbons may be employed. For example, light straight-runnaphtha may be used in some cases. Ordinarily it is preferred that aparailln be used and that it be substantially free from olens,diolefins, naphthenes and aromatics because these increase the loss offurfural by reason of the greater solubility of furfural therein duringthe extraction, because the unsaturates are not desirably inert, andbecause .these hydrocarbons are too costly for the purpose at hand.

The amount of the light hydrocarbon employed may vary within quite widelimits. In general, .the weight ratio of light hydrocarbon to oils inthe oil-furfural mixture being extracted may range from 10 to 1 to 100to 1, a ratio of from 50 to 1 to 100 to 1 often being preferred.

The amount of water employed may likewise vary widely depending upon anumber of circumstances, as explained in the copending applica- .tion ofWeinaug and Buell'above-identifled. Factors affecting the weight ratioof Water to furfural in the oil-furfural mixture being extracted includetemperature of extraction, concentration of furfural, degree ofsaturation of the water phase with furfural desired, etc. It is usuallypreferred to use a considerable excess of water over that required todissolve all of the furfural contained in the oil-furfural mixture; forexample, enough water to give a solution of furfural in water which isinot over 50% saturated ranging down to 10% saturated at the extractiontemperature. Use of .too much Water is undesirable because it requiresan excessive amount of heat to carry tbut; thedistillation applied tothe Waterfurfural mixture to obtain the furfural-water azeotrope as theoverhead product.

The extraction may be conducted at temperatures ranging in the extremefrom 50 to 300 degrees F. but preferably 90. to degrees F. Theadvantages of moderate temperatures are set forth in detail in thecopending application of Weinaug'and Buell referred to above. While itis possible to carry out the extraction at tempera- .tures equal to orabove the critical solution Itemperature for proportions of Water andfurfural, it would not normally be completely desirable. It is preferredto use such a proportion of water that all of the furfural can dissolve.therein at moderate temperatures of not over 150 F., since much betterrecovery of furfural from oil' is thereby obtained, the loss of furfuralin solution in the oil phase being at a minimum. Another advantage ofthe use of an excess of water, so that a dilute aqueous phase withrespect to furfural results', is that the solubility of oil in such adilute aqueous phase is very low whereas as the aqueous phase becomessaturated with furfural the solubility of oil therein increases.`Another advantage of the use o1' moderate temperatures, i. e. not over150 F., is that the amount of oil dissolved in the aqueous phase isminimized since the solubility of oil in aqueous furfural rises withincreasing temperature.

The pressure at which the extraction is conducted may depend somewhat onthe tempera- .ture but usually ranges from atmospheric to moderatelysuperatmospheric. The extraction is generally conducted in closedpressure-resisting equipment in order .to minimize losses byvolatiiization. The pressure is generally suilicient to maintain all ofthe light hydrocarbon employed in the liquid state, that is, eitherdissolved in the oil phase or as a separate liquid phase.

The water extraction may be carried out in any suitable way, forexample, by intimately mixing the water, furfural-oii mixture and lighthydrocarbon in a mixing pump or other adequate mixing means and thenallowing the resulting mixture to separate into two phases or layers ina settling zone or chamber or by continuously countercurrentlycontacting the water extractant and the furfural-oii mixture in thepresence of the light hydrocarbon which in such case is usuallydissolved in the furfural-oil mixture, in a column equipped with theusual contacting means such as bubble caps, packing, etc. The operationmay be either single stage orl multistage and may be carried out eitherbatchwise or continuously. The two phases. namely, extract and rainate,are separately withdrawn in the usual manner.` The hydrocarbon phase isfractionally distilled to separate as an overhead the light hydrocarbonfrom a bottoms product of the oil contaminants originally present in thefurfural. The water-furfural phase is also subjected to fractionaldistillation to separate the azeotrope of furfural and water overheadfrom a bottoms product composed essentially of the remainder of thewater which i is recycled to the water extraction unit in order to savewater and the small amount of furfural which may be dissolved therein.The overhead vapors are cooled and totally condensed and the condensatecaused to form two separate liquid layers. The upper layer is composedof water saturated with furfural at the existing temperature and istotally reiluxed to the azeotrope co1- umn while the lower layerconstitutes the oil-free furfural productsl or jme,lirwlention..y

The light hydrocarbon obtained by distillation of the hydrocarbon phaseis recycled to the extraction unit either directly or by recycling tothe unit wherein the furfuralis extracted with light hydrocarbon; in thelatter case the light hydrocarbon ultimately appears in the feed to theprocess of the present invention. The process of the present inventionis preferably carried out under such conditions that the hydrocarbonphase (rafllnate) does not contain more than 3 weight per cent offurfural and that the extract phase does not contain more than 0.1weight per cent of oil. excessive loss of furfural and the latterspecication insures that the purified furfural product contained notover 0.1 weight per cent of hydrocarbon. y

'I'he process of the present invention is applicable to anyoil-furi'ural mixture. The light hydrocarbon may be already present inthe oil-,furfural mixture or it may be added in any suitable way in thezone in which the water extraction is conducted. The invention isespecially applicable to the oil-furfural mixture obtained by theextrac- 'Ihe former limitation insures against 6 tion of oilcontaminated furfural with a light hydrocarbon solvent as disclosed inthe copending application of Thodos and Weinaug, Ser. No. 546,371, iledJuly 24, 1944. In such case most of the contaminating oils present inthe furfural by reason of their greater solubility in the lighthydrocarbon extractantappear in the light hydrocarbon phase. Somefurfural is also dissolved in the light hydrocarbon phase. The presentinvention is readily applicable to such a light hydrocarbon phase torecover the furfural content thereof.

The invention may also be applied to thelight hydrocarbon extractobtained from extraction of a furfural-oil-polymer mixture to free itfrom polymer in accordance with the copending application of January 12,1945. The polymer-free extract resulting from such a process 4may betreated in such manner as to effect separation into a predominatelylight hydrocarbon phase containing most of the oil and some furfural anda purified i'urfural phase relatively free from oil. The lighthydrocarbon phase so obtained may be employed as the feed to the presentinvention.

It has been found that vthe presence of a light hydrocarbon in the waterextraction of furfural from oil greatly Vfacilitates such an extraction.It brings about sharper separation into a waterfurfural-rich phase and ahydrocarbon-rich phase. The amount of furfural dissolved in thehydrocarbon phase is considerably reduced and the amount of hydrocarbondissolved in the water-furfural-rich phase is likewise greatly loweredby reason of the presence of the lighthydrocarbon in .accordance with`the present invention. 'I'he light hydrocarbon prevents emulsificationbetween the hydrocarbon phase and the waterfurfural phase, permitsshorter settling time and more effective separation between furfural andoily contaminants.

The invention will be more readily understood by referring to theaccompanying drawing which .shows one possible modification. In `thedrawing, the feed maybe Iderived from a furfural purication processwherein light hydrocarbon is used for separating the hydrocarboncontaminants from the furfural. The hydrocarbon-rich phase, containing asmall amount of furfural before removal of the light hydrocarbontreating agent, enters via line i and is intimately mixed with waterentering via line 2 and fed into extraction settler 3 where two-phaseseparation occurs. If desired, a mixing pump 4 may be interposed forthepurpose of effecting intimate admixture of the water and the feed. Insettler 3 a hydrocarbon-rich phase, greatly reduced in furfural content,is obtained as the top layer and a water-furfural-rich phase as thebottom layer. The hydrocarbon-rich phase is fed via line 5 tofractionator 6 `where the light hydrocarbon treating agent is recoveredas the overhead product. 4The overhead product is condensed, a portionis refiuxed to column 6 and the remainder is recycled via lines 'i and 8to the furfural purification process (not "shownl, The bottomproductfrom fractionator 6 is withdrawn via line 9 and consistsprimarily of the hydrocarbon contaminant greatly reduced in furfuralcontent.

Thev water-furfural phase from settler 3 is `withdrawn via line i0 andfed to azeotrope col.-

umn I i wherein there is taken overhead the azeotrope of water andfurfural. The overhead is completely condensed and allowed to separateGeorge Thodos. Ser. No. 572,532, filed l and is totally reiluxed vialine I3.

into two layers in accumulator I2. The upper layer consists of watersaturated with furfurai The lower layer consists of furfural saturatedwith water and is withdrawn via line Il as the product of the process,The bottoms product from column I I is composed essentially of water andis recycled via lines I and 2 to the extraction unit. If desired, makeupwater may be introduced to the system vla line I6. In situations wherethe incoming feed does not contain a light hydrocarbon or does notcontain a sufficient concentration of a light hydrocarbon, lighthydrocarbon is introduced'to the water extraction system vial line l1.If desired, a portion or all of the light hydrocarbon flowing in line 'Imay be recycled directly to the water extraction system by means oflines I 8 and I1.

Emmiple A hydrocarbon-furfural mixture derived by treating contaminatedfurfural with a light hydrocarbon, n-pentane, in the manner describedabove to remove the hydrocarbon contaminants was intimately mixed withwater and introduced into extraction settler 3. The composition ofthehydrocarbon-furfural mixture was:

Furfuraipounds-- 6.1 Water do Trace Heavy oils dn 1.2 Normal pentane92.7

Four hundred sixty pounds of water were used per 100 pounds ofv feed ofthe above composition.

was returned to fractionator 6 as reflux. The l remaining portion wasrecycled via lines 'l and 8 to steps (not shown) for removing relativelyheavy hydrocarbon contaminants from furfural.

covery of valuable furfural.

tion is accomplished more easily andwith less The bottom phase fromextraction-settler I3 was fed to water-furfu'ral fractionator II. Inthis fractionator a furfural-water azeotrope was taken overhead,condensed,'coo1ed. and collected in accumulator I2. Two liquidphases'separated in accumulator I2; the upper phase was water- Water wasintroduced at the top and the hydro-l carbon-furfural-rich mixture atthebottom in each case. The remaining equipment was the same as inthe abovedescribed modification. In the three-stage countercurrent arrangementthe amount of water required to effect the removal of the same amount offurfural from pounds oi feed as in the above example was about 11 0pounds. i

From the foregoing it will be seen that the present invention presentsnumerous advantagesover simple water extraction in the absence of a ghthydrocarbon as disclosed in the copending gpplication of Weinaug andBuell referred to above. The process of the present invention bringsabout a sharper separation between furfural and oil and substantiallyreduces the loss of iurfural, correspondingly increasing the re- Thevphase separaemulsification and in a shorter time. Other advantages ofthe process of the present invention will be apparent to those skilledin the art.

I claim:

1. The process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be diillcult toseparate from furfural by distillation which comprises subjecting suchfurfural-hydrocarbon mixture to water extraction in the presence of aliquid hydrocarbon having a boiling point substantially lower than the`boiling point of furfural.

2. The process for recovering furfural from admixtu're with hydrocarbonshaving boiling points so close to that of' furfural as to be difdcult toseparate from furfural by distillation which comprises subjecting suchfurfural-hydrocarbon mixture to water extraction yin the presence of aliquid hydrocarbon having not more than 8 carbon atoms per molecule i 3.'I'he process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be dii'iicultto separate from furf'ural by distillation which comprises subjectingsuch furfural-hydrocarbon mixture to water extraction in the presence ofa liquid aliphatic hydrocarbon having from 3 to 8 carbon atoms permolecule.

4. The process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be diicult toseparate from furfural by distillation which comprises subjecting suchfurfural-hydrocarbon mixture to water extraction in the presence of aliquid paraffin hydrocarbon having from 3 to 8 carbon atoms permolecule.

5. The process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be difficult toseparate from furfural by distillation which comprises subjecting suchturfural-hydrocarbon mixture to water extraction in the presence ofliquidnormal pentane.

6. The process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be diflicult toseparate' from furfural by distillation which comprises-subjecting suchfurfural-hydrocarbon mixture to water extraction ln the presence of aliquid hydrocarbon having a boiling point substantially lower than thatof furfural, separately withdrawing the resulting aqueous phase and theresulting hydrocarbon phase, subjecting said aqueous phase to fractionaldistillation in a fractionation column and thereby separating it into anoverhead fraction of furi'ural and water in azeotropic proportions and abottoms fraction of water, condensing said overhead and causing theliquid condensate to separate into a water phase and a furfural phaseessentially free of hydrocarbons, withdrawing said water phase andrefluxing said column therewith, and separately withdrawing saidfurfural phase as the product of the process.

7. The process for recovering furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be difficult toseparate from furfural by distillation which comprises subjecting suchfurfural-hydrocarbon mixture to water extraction in the presence of aliquid paraln hydrocarbon having from 3 to 8 carbon atoms per molecule,separately withdrawing the resulting aqueous phase and the resultinghydrocarbon phase, subjecting said aqueous phase to fractionaldistillation in a fractionation co1- umn and thereby separating it intoan overhead fraction of furfural and water` in azeotropic proportionsand a bottoms fraction of water, condensing said overhead and causingthe liquid condensate to separate into a water phase and a furfuralphase essentially free of hydrocarbon, withdrawing said water phase andrefiuxing said column therewith, separately withdrawing said furfuralphase as the product of the process, and subjecting said hydrocarbonphase to vfractional distillation to separate as an overhead saidhydrocarbon having from 3 to 8 carbon atoms per molecule from a. bottomsproduct of said hydro- -carbons having boiling points close to that oi'furfural.

8. 'I'he process for recovering furfural from admixture withhydrocarbons having boiling points so close to that of furfural as to bediftlcult to separate from furfural by distillation which comprisessubjecting such furfural-hydrocarbon mixture to water extraction in thepresence of a liquid paraiiln hydrocarbon having from 3 to 8 carbonatoms per molecule, the amount of said parain hydrocarbon being such asto give a weight ratio of said paramn hydrocarbon to said hydrocarbonshaving boiling points close to that of furfural of from 10 to 1 to 100to 1, said water ing hydrocarbon phase, subjecting said aqueous phase tofractional distillation in a fractionation column and thereby separatingit'into an overhead fraction of furfural and water in azeotropicproportions and a bottoms fraction of water, condensing said overheadand causing the liquid condensate to separate into a water phase and aiurfural phase essentially free of hydrocarbon, withdrawing said waterphase and refluxing said column therewith, separately withdrawing saidfurfural phase as the product of the process, and subjecting saidhydrocarbon phase to fractional distillation to separate as an overheadsaid paraflin hydrocarbon having from 3 to 8 carbon atoms per moleculefrom a bottoms fraction of said hydrocarbons having boiling points closeto that of furfural.

9. The process for recovering `furfural from admixture with hydrocarbonshaving boiling points so close to that of furfural as to be difilicultto separate from furfural by distillation which comprises subjectingsuch furfuralhydrocarbon mixture to water extraction in the presence orliquid normall pentane, the amount of said-normal pentane being such asto give a weight ratio of normal pentane to said hydroextraction beingVconducted at a temperature ranging from to 150 F., separatelywithdrawing the resulting aqueous phase and the resultcarbons havingboiling ponts close to .that of furfural of from 10 to 1 to 100 to 1,conducting said water extraction at a temperature o1' from 90 to 150F.,separate1y withdrawing the resulting aqueous phase and the resultinghydrocarbon phase, subjecting said aqueous phase to fractionaldistillation in a fractionation column and thereby separating it into anoverhead fraction of furfural and water in azeotropic proportions and abottoms fraction of water, condensing said overhead and causing theliquid condensate to separate into a water phase and a furfural phaseessentially free of hydrocarbon, withdrawing said water phase andrefluxing said column therewith, recycling a bottoms fraction of waterto said extraction step, subjecting said hydrocarbon phase to fractionaldistillation to separate an overhead of normal pentane from a. bottomsproduct of said hydrocarbons having boiling points close to that offurfural; and re-v cycling said normal pentane to said water extraction.

BERTRAND JESSE MAYLAND.

